Preparation and characterization of thermally and electrically triggered shape memory SEBs-G-MA/ PCL/ graphene polymer composites

Smart materials constitute an important part of advanced material research. Stimuli-responsive polymers are materials that can significantly change their properties such as shape, mechanical properties, phase separation, optical and electrical properties, surface, and permeability due to small changes occurring in environmental conditions such as temperature, electric field, pH, light, magnetic field, and solvent. In recent years, shape memory polymers (SMPs), one of the evolving types of smart materials, have the ability to change their shapes through stimuli such as heat, electricity, and light.In this study, electro-active shape memory polymer composites were developed by adding graphene nano plate (GNP) filler to a shape memory polymer blend containing 60/40 weight percent of maleic anhydride grafted poly(styrene-b-ethylene-butylene-b-styrene) (SEBS-g-MA), a thermoplastic elastomer, and a semi-crystalline polyester poly(ε-caprolactone) (PCL) to impart electrical stimulation property. Polymer composites containing 5 phr, 10 phr, 20 phr, and 30 phr of GNP were prepared using the solution mixing technique. The effects of the produced composites on the electrical, shape memory, thermal, and mechanical properties of the polymer blend were investigated. Morphological analysis performed with scanning electron microscopy (SEM) revealed that the graphene filler was homogeneously distributed within the polymer matrix. It was observed that as the amount of graphene increased, the graphene filler had a significantly large volume in the composites containing 10 phr, 20 phr, and 30 phr of GNP and provided a homogeneous distribution throughout the polymer matrix.While the composite containing 5 phr of GNP showed improvements in elastic modulus, tensile strength, elongation at break, and toughness compared to the polymer blend, at higher filler loadings, although the elastic modulus values increased proportionally, decreases were obtained in other properties.In the DSC analysis, while the melting temperature (TmPCL) of the key phase of the shape memory polymer matrix, PCL, was hardly affected by the presence of GNP filler, an increase in crystallization degrees was observed due to the nucleation effect of GNP filler, and it was determined that crystallization temperatures shifted to higher values. The results of dynamic mechanical analysis showed that the GNP filler increased the glass transition temperature of the ethylene/butylene block of the SEBS-g-MA elastomer and, on the other hand, improved the storage modulus and damping parameter values of the polymer matrix at 25°C. It was determined that the creep resistance improved as the amount of GNP increased based on the creep tests conducted. In shape memory performance measurements, all composites exhibited shape fixity ratios higher than 92% and shape recovery ratios higher than 80%. The electrical resistance of the polymer matrix decreased as the GNP filler increased, and the lowest electrical resistance was measured as 834.1 Ω.cm for the composite containing 30 phr of GNP. It was determined that the same composite reached body temperature under a voltage of 23 V and the shape transformation temperature of 65°C under a voltage of 48 V. The composite with 30 phr content achieved a electro-active shape recovery of 95.12% to the initial shape after 180s under 48V voltage.